FIG. 1 is a schematic diagram of a prior art closed loop electro-mechanical servo system that converts signals from a magnetic azimuth detector 14 (MAD) into the corresponding digital signals 15. This electro-mechanical system essentially converts three-wire data representing analog electrical angles from a flux valve (MAD) to an equivalent mechanical shaft angle and then generates a digital representation of the mechanical angle.
The electro-mechanical servo system comprises a synchro control transformer 10 (CT) that accepts, at its three-wire stator terminals, a set of carrier frequency signals (nominally 800 Hz) from the flux valve 14 excited by a 400 Hz reference. The CT 10 produces, at its rotor terminals, a carrier frequency signal proportional to the sine of the angular difference (sin(.theta.-.o slashed.)) between the electrical input angle, .theta., and the mechanical angular position of the CT shaft, .o slashed.. Since the flux valve signals are distorted by the harmonics of the reference and fundamental frequencies, the CT 10 is "tuned" by capacitors on its rotor terminals.
The capacitors create a bandpass filter with a maximum amplitude response at the frequency of interest as the circuit is at or near the resonant condition. This filtered signal is then processed to control a motor 11, which drives the shaft of the CT 10, and the shaft of a synchro control transmitter 12 (CX) until sin(.theta.-.o slashed.) goes to zero, indicating the mechanical angle equals the electrical angle.
The shafts of the CT 10 and CX 12 are connected to the motor 11 by a mechanical linkage such that their reference shaft positions are the same. The CX 12 accepts an AC reference excitation at its rotor terminals and develops at its stator terminals a three-wire AC output at the reference frequency. The amplitude ratios of the line-to-line voltages of this three-wire output are a function of the angular position of the shaft. These signals are supplied to the synchro-to-digital converter 13 (S/D) which produces a digital representation of the electrical angle .theta. for use by the processor.
The servo mechanism shown in FIG. 1 is susceptible to failure due to repeated use and resulting degradation of the mechanical components. A need exists, therefore, for a purely electrical MAD converter system which eliminates the mechanical components and thus has an increased reliability.